A tree bog is a form of outside toilet which has willows, nettles and other nutrient-hungry flora planted around it. ‘Bog’ is a British English slang word for ‘toilet,’ not to be confused with its other meaning of ‘swampland.’ The feces are held in a chamber open to the air which allows it to decompose rapidly, feeding the trees around it. Unlike a conventional compost toilet, a tree bog should never need emptying. Effectively, it is a system for converting human waste to biomass.
The tree bog was invented in 1995 by Jay Abrahams of Biologic Design in the UK after he observed that the trees around the place where feces were deposited were particularly vigorous. Tree bogs can be considered examples of permaculture design (which seeks to develop sustainable human settlements). The tree bog is a simple method of composting wastes, and since its introduction over 500 have been built in Britain. They have been on sites ranging from fruit farms and pick-your-own enterprises, campsites, and an angling lake, to annual festival sites, remote/low impact dwellings, holiday cottages, and churches.
The tree bog has also attracted the attention of NGOs and aid workers who hope to develop its potential for shanty towns or refugee camps – anywhere that water is scarce and the population pressure on resources is high. Most regions have and useful plants which, if willow is not available, can be used.
A tree bog is simply an uncontrolled compost heap whose function has been enhanced by use of moisture/nutrient-hungry trees. Tree bogs use no water, purify waste as they create willow as a biomass resource, and also contain the organic waste, thus preventing the spread of disease – all whilst creating soil. A seating platform/cubicle is mounted at least one meter high. The area beneath the seating platform should be enclosed by a double-layer of chicken wire – this acts as an effective rodent/small animal and child proof barrier, but allows air to circulate through the compost heap. The space between the wire should be stuffed not too densely with straw which acts as a wick to help sop up excess urine preventing the likelihood of odor problems due to incomplete biological absorption of the nitrogen from the urine. The straw filled wire also enables the pile to be well-aerated whilst acting as a visual screen for the first year’s use.
The structure is then surrounded by two closely planted rows of osier or biomass willow cuttings; this living wall of willow can be woven into a hurdle-like structure and its annual growth can be harvested. Tree bogs can also be sited on the edge of existing stands of trees, woodlands or hedges: the mature tree roots will soon find the additional source of nutrients, so that the willow may be unnecessary, – or indeed, in the middle of a mature woodland, pretty well impossible due to shading.
The Daily Omnivore 
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